Non-woven fabric for separator of alkali cell and method for production thereof

ABSTRACT

The present invention provides a non-woven fabric for an alkaline battery separator comprising semi-aromatic polyamide fibers comprising a dicarboxylic acid component, in which 60 mol % or more of the dicarboxylic acid component is an aromatic carboxylic acid component, and a diamine component, in which 60 mol % or more of the diamine component is an aliphatic alkylene diamine having 6 to 12 carbon atoms, and ethylene/vinyl alcohol copolymer fibers; wherein, the separator non-woven fabric has superior alkaline resistance in which the weight loss rate after 20 days is 5% or less in an alkaline resistance test at 90° C. in aqueous KOH solution having a specific gravity of 1.30. Consequently, since the present invention enables rapid charging and large-current discharging while also allowing thickness to be reduced for higher capacity, it can be preferably used as a non-woven fabric for an alkaline battery separator.

TECHNICAL FIELD

The present invention relates to a non-woven fabric for an alkalinebattery separator that can be preferably used in an alkaline secondarybattery such as a nickel-cadmium battery, nickel-zinc battery,nickel-hydrogen battery or others, and a method for producing the same.More particularly, the present invention relates to a non-woven fabricfor an alkaline battery separator that allows rapid charging and largecurrent discharge, has a thin thickness enabling high capacity, and hassuperior alkaline resistance, and a method for producing the same.

BACKGROUND ART

Since alkaline secondary batteries comprising a positive electrode,separator and negative electrode have superior charging and dischargingcharacteristics, superior overcharging and over-dischargingcharacteristics, and can be used repeatedly owing to their long life,they are widely used in electronic equipment having extremely small sizeand weight. Non-woven fabric used in alkaline battery separators isknown to fulfill roles that include separation of the positive andnegative electrodes, prevention of short-circuit, retention ofelectrolyte, and permeation of gas generated by the electrode reactions.Consequently, this non-woven fabric is required to have alkalineresistance, hydrophilicity, liquid retention and oxidation resistancewith respect to the electrolyte, and heat resistance with respect to theworking temperature. In addition, a non-woven fabric for alkalinebattery separators is also required to be provided with runningstability when in a wound configuration in addition to mechanicalproperties such as tensile strength so as to be able to oppose thetension applied in the battery production process.

In recent years, in addition to allowing rapid charging and largecurrent discharge, alkaline secondary batteries have also come to berequired to have larger capacities. Increasing battery capacity can berealized by increasing the amounts of positive electrode active materialand negative electrode active material. Consequently, attempts have beenmade to reduce the thickness of the separator by lowering the weightingcapacity, namely the basis weight, of the separator non-woven fabric.However, if the thickness of the separator is reduced by lowering thebasis weight of the separator non-woven fabric, since the liquidretention of the separator typically decreases, the life of theseparator non-woven fabric shortens due to drying of the liquidresulting from repeated charging and discharging. In the case of drynon-woven fabric in particular, lowering of the basis weight causes aconsiderable loss of non-woven fabric uniformity, thereby increasing thesusceptibility to short-circuit between the positive and negativeelectrodes and lowering leakage resistance. In addition, even in thecase of a wet non-woven fabric, there is the risk of being unable toemploy a wound configuration due to the significant reduction in tensilestrength.

In consideration of the aforementioned reasons, the basis weight ofnon-woven fabric for alkaline battery separators is typically within therange of 50 to 80 g/m² and the thickness is typically within the rangeof 120 to 200 μm, and the capacity of alkaline secondary batteries wasunable to be significantly improved.

On the other hand, a non-woven fabric using aliphatic polyamide fiberssuch as fibers made of Nylon 6 or Nylon 66 has come to be used as anon-woven fabric for alkaline battery separators that has superiorhydrophilicity and liquid retention with respect to electrolyte and lowelectrical resistance when containing electrolyte. Alkaline secondarybatteries using this aliphatic polyamide fiber non-woven fabric havesuperior alkaline resistance, high hydrophilicity and superiorelectrolyte retention, while also having the characteristic of superiordischarge characteristics for large currents. However, this non-wovenfabric lacks chemical stability, and has inferior heat resistance asrepresented with the glass transition temperature as well as inferioroxidation resistance at high temperatures in particular. Consequently,it has the disadvantage of being susceptible to oxidation anddecomposition by oxygen gas generated during charging of the alkalinesecondary battery, and causes a significant decrease in batteryperformance when the alkaline secondary battery is used undertemperature conditions within the range of 60 to 80° C. Thus, alkalinesecondary batteries in which an aliphatic polyamide fiber non-wovenfabric is used for the separator non-woven fabric demonstrate largeself-discharge caused by decomposition of the non-woven fabric, andparticularly in the case of alkaline secondary batteries that undergorepeated charging and discharging at high temperatures, the cycle lifeis shortened considerably.

On the other hand, polyolefin fiber non-woven fabric has been used inalkaline secondary batteries requiring heat resistance at comparativehigh temperatures. Although polyolefin fiber non-woven fabric hassuperior heat resistance, since it is hydrophobic, it is resistant towetting by electrolyte and has a low electrolyte retention volume.Consequently, this non-woven fabric has high electrical resistance whenused as the separator non-woven fabric of an alkaline secondary battery,and is inferior in terms of rapid battery charging and large currentdischarge as compared with polyamide fiber non-woven fabric. Inaddition, since there is the risk of electrolyte retained between thefibers being pushed out from inside the separator due to the pressure ofoxygen gas generated from the positive electrode during charging,eventually causing the positive electrode to expand due to repeatedcharging and discharging, there is the risk of the occurrence of dry outin cases in which the liquid retention of the alkaline battery separatornon-woven fabric is insufficient.

Therefore, attempts have been made to treat alkaline battery separatornon-woven fabric that uses polyolefin fibers with a surfactant. However,there are problems with the stability of the surfactant in electrolyte.In addition, since the surfactant is released when the period whilerepeated charging and discharging is in progress has elapsed, this hasnot led to adequate improvement of absorption and retention ofelectrolyte.

In order to solve the problem of hydrophobicity of alkaline batteryseparator non-woven fabric composed of a polyolefin fiber non-wovenfabric, numerous methods have been proposed for improving absorption orretention of electrolyte by imparting hydrophilicity to the polyolefinfibers. For example, sulfonation treatment consisting of treatment withhot conc. sulfuric acid, fuming sulfuric acid or chlorosulfuric acid isdisclosed in Japanese Unexamined Patent Publication No. Sho. 56-3973 andJapanese Unexamined Patent Publication No. Sho. 58-175256, while amethod in which the structural surface of non-woven fabric is modifiedby fluorine treatment by treating with a gas containing fluorine,acrylic acid graft polymerization treatment in which groups having ahydrophilic group such as in acrylic acid or methacrylic acid are graftpolymerized, corona discharge treatment or reducing fiber diameter andso forth is disclosed in Japanese Unexamined Patent Publication No. Hei.1-132042. However, since the hydrophilic treatment methods described inthese examples of the prior art cause a considerable decrease instrength in the alkaline battery separator non-woven fabric, causedeterioration of the appearance or attempt to reduce thickness bylowering the basis weight, they have problems including difficulty inenabling stable industrial production.

Therefore, inventions that use aromatic polyamide fibers or completelyaromatic polyamide fibers for the alkaline battery separator non-wovenfabric instead of aliphatic polyamide fibers are disclosed in, forexample, Japanese Unexamined Patent Publications Nos. Hei. 5-283054,Sho. 53-58636 and Sho. 58-147956. Non-woven fabric composed of aromaticpolyamide fibers or completely aromatic polyamide fibers typically havesuperior hydrophilicity as well as superior alkaline resistance andoxidation resistance. However, due to their high heat resistance, theadhesiveness itself of a non-woven fiber formed only of these fibers islow, and since the adhesiveness with typical thermoplastic binder fibersis particularly low, the non-woven fabric strength is inadequate.Although methods that use an adhesive resin have been considered forimproving adhesiveness, when a non-woven fabric adhered according tothese methods is used as a battery separator, there is the risk of theadhesive resin dissolving in the battery electrolyte.

So-called semi-aromatic polyamide fibers have been proposed to improveon the problem of adhesiveness. An alkaline battery separator that usesa semi-aromatic polyamide fiber (MXD-6 fiber) non-woven fabric formedfrom aromatic diamine and aliphatic dicarboxylic acid has inferioroxidation resistance at high temperatures, and may deteriorate as aresult of being oxidized by oxygen gas generated during charging. On theother hand, semi-aromatic polyamide fibers formed from aliphatic diamineand aromatic dicarboxylic acid being able to be preferably used inbattery separators as fibers having hydrophilicity, alkaline resistanceand oxidation resistance is disclosed in, for example, JapaneseUnexamined Patent Publications Nos. Hei. 9-259856 and 2002-151041.

However, semi-aromatic polyamide fibers formed from aliphatic diamineand aromatic dicarboxylic acid have low fiber strength and leakageresistance cannot be said to be adequate. In addition, since they alsohave high heat resistance in the same manner as aromatic polyamidefibers, it is necessary to mix them with thermoplastic binder resinfibers such as polyolefin fibers or others to increase adhesivenessbetween fibers and enhance the non-woven fiber strength. However, sincethe melting point of the thermoplastic binder resin is lower than thetemperature environment in alkaline secondary batteries are used inlarge equipment (160° C. or higher), there is the risk of having adetrimental effect on long-term stability of the battery separator.

In this manner, semi-aromatic polyamide fiber non-woven fabric ispromising as a non-woven fabric for alkaline battery separators.However, problems still remain with respect to adhesiveness with binderresin fibers, leakage resistance, further inhibition of self-dischargephenomena, and improving yield during alkaline secondary batteryproduction in the case of reducing thickness by lowering the basisweight of the separator non-woven fabric. Moreover, this non-wovenfabric is also unable to effectively respond to severe requirements forincreasing battery capacity on the premise of rapid charging and largecurrent discharge. Therefore, the object of the present invention is toprovide a non-woven fabric for an alkaline battery separator, which isbased on the use of a semi-aromatic polyamide fiber non-woven fabric,allows rapid charging and large current discharge, enables thickness tobe reduced for higher battery capacity, and has superior alkalineresistance and a method for producing the same.

DISCLOSURE OF THE INVENTION

As a result of extensive research to solve the aforementioned problems,the inventors of the present invention invented a non-woven fabric foran alkaline battery separator that is based on the semi-aromaticpolyamide fiber non-woven fabric of the present invention, and a methodfor producing the same.

Namely, the present invention relates to a non-woven fabric for analkaline battery separator comprising semi-aromatic polyamide fibersformed from a dicarboxylic acid component in which 60 mol % or more ofthe dicarboxylic acid component is an aromatic carboxylic acidcomponent, and a diamine component in which 60 mol % or more of thediamine component is an aliphatic alkylene diamine having 6 to 12 carbonatoms, and binder fibers in the form of ethylene/vinyl alcohol copolymerfibers, wherein the separator non-woven fabric has superior alkalineresistance in which the weight loss rate after 20 days is 5% or less inan alkaline resistance test at 90° C. in aqueous KOH solution having aspecific gravity of 1.30.

In a non-woven fabric for an alkaline battery separator of the presentinvention, the semi-aromatic polyamide fibers are preferably 60 to 95%by weight, and the ethylene/vinyl alcohol copolymer fibers arepreferably 5 to 40% by weight. In addition, the ethylene/vinyl alcoholcopolymer fibers preferably have a mono-filament fineness (diameter ofthe monofilament) of 0.01 to 0.5 dtex, and the semi-aromatic polyamidefibers are preferably formed from a dicarboxylic acid componentcomprising a terephthalic acid component and a diamine componentcomprising a 1,9-nonane diamine component or a mixture of that and a2-methyl-1,8-octane diamine component.

In addition, in the present invention, in addition to semi-aromaticpolyamide fibers and binder fibers, division type composite fibers arepreferably also contained that are formed from semi-aromatic polyamideand at least one type of polymer selected from the group consisting ofpoly-phenylene sulfide, polymethylpentene and polypropylene.

Moreover, in the present invention, in addition to the semi-aromaticpolyamide fibers and binder fibers, non-stretched semi-aromaticpolyamide fibers or high-strength fibers are preferably also contained.

A non-woven fabric for an alkaline battery separator of the presentinvention preferably also has a basis weight of 45 g/m² or less,thickness of 100 μm or less, tensile strength of 1960 N/m or more,maximum pore diameter of 50 μm or less, and average pore diameter of 20μm or less.

In addition, a method for producing a non-woven fabric for an alkalinebattery separator contains a step of preparing a dispersed slurrycontaining a mixture of semi-aromatic polyamide fibers andethylene/vinyl alcohol copolymer fibers, a step of producing a rawfabric from the dispersed slurry using a wet papermaking method, and astep of subjecting to hydrophilic treatment and calendaring treatment onboth sides of the raw fabric. This dispersed slurry more preferablycomprises a dispersed slurry in which division type composite fibers,preliminarily split into at least two types of ultrafine fibers with arefining machine, are additionally contained.

BEST MODE FOR CARRYING OUT THE INVENTION

The following provides a detailed explanation of a non-woven fabric foran alkaline battery separator of the present invention.

A non-woven fabric for an alkaline battery separator of the presentinvention contains semi-aromatic polyamide fibers prepared from adicarboxylic acid component, in which 60 mol % or more of thedicarboxylic acid component is an aromatic carboxylic acid component,and a diamine component in which 60 mol % of the diamine component is analiphatic alkylene amine having 6 to 12 carbon atoms, and ethylene/vinylalcohol copolymer fibers. This separator non-woven fabric has superioralkaline resistance in which the weight loss rate after 20 days is 5% orless in an alkaline resistance test at 90° C. and aqueous KOH solutionhaving a specific gravity of 1.30.

As a result of using semi-aromatic polyamide fibers, the separatornon-woven fabric has superior chemical stability such as alkalineresistance and oxidation resistance, and has the characteristic of lowelectrical resistance in the state of containing electrolyte.Consequently, discharge characteristics at large current can be improvedwithout having a detrimental effect on self-discharge or cycle lifecaused by fiber deterioration and decomposition. In addition, as aresult of using ethylene/vinyl alcohol copolymer fibers preferablyhaving a mono-filament fineness of 0.01 to 0.5 dtex for the binderfibers, the separator non-woven fabric is able to demonstrate tensilestrength and hardness capable of opposing battery assembly machinery bypowerfully holding together the composite fibers without increasing theinternal resistance of the non-woven fabric for an alkaline batteryseparator, and without crushing the voids in the non-woven fabric orimpairing retention of electrolyte.

Furthermore, the alkaline resistance of a non-woven fabric for analkaline battery separator has an effect on the cycle lifecharacteristics of the battery. Amidst growing requirements to increasebattery capacity and increase battery output, the temperature that isreached inside the battery due to the charging and discharging cycle istending to become even higher. Deterioration of a battery separatornon-woven fabric caused by its decomposition in a high-temperatureaqueous alkaline solution lowers the liquid retention of the separatornon-woven fabric and impairs the function of the active material orcadmium as a protective film of dendride growth, thereby acceleratingdeterioration of cycle life.

Thus, the alkaline resistance of a separator non-woven fabric ispreferably such that the weight loss ratio of the non-woven fabric at90° C. and aqueous KOH solution having a specific gravity of 1.30 iswithin 1% after 7 days, within 2% after 14 days and within 5% after 20days. In the case the weight loss ratio of the separator non-wovenfabric after 20 days is within 5%, decreases in strength and liquidretention of the separator non-woven fabric as well as the occurrence ofincreases in pore diameter can be prevented, thereby making it possibleto secure a longer cycle life.

A non-woven fabric for an alkaline battery separator of the presentinvention preferably has tensile strength of 1960 N/m or more in orderto oppose the tension of automatic winding assembly machines. If thetensile strength is greater than or equal to 1960 N/m, the separatornon-woven fabric is able to withstand the tension of automatic windingassembly machines, thereby allowing it to be reliably wound since theoccurrence of short-circuit can be prevented, even if the width becomesnarrow, without breaking.

In addition, pore diameter of a non-woven fabric for an alkaline batteryseparator has an effect on leakage resistance and dendride resistancecharacteristics. Leakage resistance and dendride resistancecharacteristics are also dependent on the basis weight and thickness ofthe non-woven fabric, and even in cases in which the maximum porediameter exceeds 50 μm and the average pore diameter exceeds 20 μm, thenon-woven fiber can be used as a separator non-woven fabric. However, inorder to realize low basis weight and low thickness for the purpose ofincreasing battery capacity and large-current discharge, the maximumpower diameter is preferably 50 μm or less and the average pore diameteris preferably 20 μm or less. As a result, the process defect rate anddendride resistance characteristics can be kept satisfactory.

The following provides a detailed explanation of each of the compositefibers used in the present invention.

A. Semi-Aromatic Polyamide Fibers

The polyamide of the semi-aromatic polyamide fibers used in the presentinvention can be obtained by preparing from a dicarboxylic acidcomponent in which 60 mol % or more of the dicarboxylic acid componentis an aromatic dicarboxylic acid, and a diamine component in which 60mol % or more of the diamine component is an aliphatic alkylene diaminehaving 6 to 12 carbon atoms.

In consideration of the strength of the non-woven fabric and the heatresistance and chemical resistance of the separator, preferable examplesof the aromatic dicarboxylic acid component include terephthalic acid,isophthalic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,4-phenylenedioxydiacetic acid, 1,3-phenylene dioxydiacetic acid, diphenic acid,dibenzoic acid, 4,4′-oxydibenzoic acid,diphenylmethane-4,4′-dicarboxylic acid,diphenylsulfone-4,4′-dicarboxylic acid, 4,4′-biphenyl dicarboxylic acid,etc., with terephthalic acid being the most preferable. These aromaticdicarboxylic acids can be used alone or in a combination of two or moretypes.

The content of the aromatic dicarboxylic acid in the dicarboxylic acidcomponent is required to be 60 mol % or more of the dicarboxylic acidcomponent, preferably 75 mol % or more and most preferably 100%. As aresult of making the content of the aromatic dicarboxylic acid 60 mol %or more, various characteristics such as alkaline resistance, oxidationresistance and strength can be secured for the resulting fibers.

Examples of the dicarboxylic acid components other than the aromaticdicarboxylic acids include aliphatic dicarboxylic acids such as malonicacid, dimethyl malonic acid, succinic acid, 3,3-diethylsuccinic acid,glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyl-adipicacid, trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid andsuberic acid; and alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexane dicarboxylic acid, and these acidscan be used alone or in a combination of two or more types.

In addition, polyvalent carboxylic acids such as trimellitic acid,trimesic acid and pyromellitic acid may also be contained within a rangethat facilitates fiber formation and production of non-woven fabric.

In addition, 60 mol % or more of the diamine component is composed of analiphatic alkylene diamine having 6 to 12 carbon atoms. Examples of thisaliphatic alkylenediamine include linear or branched aliphatic diaminessuch as 1,6-hexanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine,2-methyl-1,5-pentanediamine, 3-methyl-1,5-pentanediamine,2,2,4-trimethyl-1,6-hexanediamine, 2,4,4-trimethyl-1,6-hexanediamine,2-methyl-1,8-octanediamine and 5-methyl-1,9-nonanediamine. Inconsideration of heat resistance, hydrolysis resistance and chemicalresistance in particular, 1,9-nonanediamine or a mixture of1,9-nonanediamine and 2-methyl-1,8-octanediamine is preferable. In amixture of 1,9-nonanediamine and 2-methyl-1,8-octanediamine, therespective molar ratios are preferably from 30:70 to 99:1, and morepreferably from 40:60 to 95:5.

The content of aliphatic alkylene diamine is required to be 60 mol % ormore of the diamine component, and in consideration of heat resistance,preferably 75 mol % or more and particularly preferably 90 mol % ormore. As a result, the oxidation resistance and strength of theresulting fibers can be improved.

The intrinsic viscosity [η]as measured at 30° C. in conc. sulfuric acidis preferably within the range of 0.5 to 2.0 dl/g, more preferably 0.6to 1.8 dl/g and particularly preferably 0.6 to 1.5 dl/g. Semi-aromaticpolyamide fibers having an intrinsic viscosity within this range havesatisfactory melt viscosity characteristics during fiber formation, andthe strength and alkaline resistance of the resulting separator aresuperior.

Furthermore, in a semi-aromatic polyamide used in the present invention,10% or more of the end groups of its molecular chain are required to besealed by an end sealing agent, preferably 40% or more of the end groupsare sealed, and more preferably 70% or more of the end groups aresealed. The resulting fibers and non-woven fabric have superiorstrength, alkaline resistance and oxidation resistance as a result ofsealing the polyamide ends. Although there are no particularrestrictions on the end sealing agent provided it is a mono-functionalcompound having reactivity with an amino group or carboxyl group on theend of a polyamide, monocarboxylic acids and monoamines are preferablein consideration of reactivity and stability of the sealed ends.

There are no particular restrictions on the production method of apolyamide of semi-aromatic polyamide fibers, and any known productionmethod can be used for producing crystalline polyamide. For example, itis possible to carry out polymerization by a liquid polymerizationmethod or interfacial polymerization that uses acid chloride and diaminefor the raw materials, a melt polymerization, solid phase polymerizationor melt extrusion polymerization that uses dicarboxylic acid and diaminefor the raw materials.

The fiber diameter of the semi-aromatic polyamide fibers is such thatthe monofilament fineness is preferably 1.5 dtex or less inconsideration of leakage resistance, liquid absorption and liquidretention, and the mono-filament fineness is more preferably 1.0 dtex orless in consideration of gas permeability and not inhibiting thehardness of the separator non-woven fabric. Furthermore, fiber diameterrefers to the value based on a circular cross-section.

The fiber length of the semi-aromatic polyamide fibers is preferably 2to 20 mm. If the fiber length exceeds 20 mm, it becomes difficult todisperse the fibers during wet papermaking, and insufficient basisweight and defective alignment occur, making it difficult to form asatisfactory raw fabric. In addition, since re-aggregation tends tooccur after the fibers have been dispersed, there is susceptibility tothe occurrence of slipping, tangling and doffing. On the other hand, ifthe fibers are less than 2 mm in length, the rupture elongation of thebattery separator non-woven fabric decreases resulting in increasedsusceptibility to breakage and tearing when subjected to pressure fromthe edges of the plates.

Although dependent on basis weight, the blending ratio of semi-aromaticpolyamide fibers in a non-woven fabric for an alkaline battery separatoris preferably 60 to 95% by weight in consideration of gas permeability,liquid absorption and charging and discharging characteristics. If theblending ratio is less than 60% by weight, since the blending ratio ofthe binder fibers increases, although the tensile strength of theseparator non-woven fabric becomes higher, electrolyte absorptiondecreases and electrical resistance increases. Consequently, theinternal resistance of the alkaline secondary battery increasesresulting in a decrease in charging and discharging characteristics. Onthe other hand, if the blending ratio exceeds 95% by weight, since theblending ratio of the binder fibers decreases, the tensile strength ofthe non-woven fabric decreases and leakage resistance becomes poor.Consequently, it becomes difficult crush the non-woven fabric byreducing its thickness.

B. Ethylene/Vinyl Alcohol Copolymer Fibers

In the present invention, ethylene/vinyl alcohol copolymer fibers havinghigh hydrophilicity and hygrothermal adhesiveness under low-temperaturepressure are used as binder fibers.

The fiber diameter is such that the mono-filament fineness is preferably0.01 to 0.5 dtex. If the mono-filament fineness exceeds 0.5 dtex, sincethe number of fibers per unit volume decreases, it becomes necessary toincrease the blending ratio of the binder fibers. In addition, since themoisture content of the wet paper roll during wet papermaking decreases,stable fabric production becomes difficult. In the case the monofilamentfineness is less than 0.01 dtex, in addition to worsening of themechanical properties and durability of the fibers themselves, it alsobecomes difficult to disperse the fibers during wet papermaking.

As a result of using ultrafine fibers within the aforementioned rangefor the ethylene/vinyl alcohol copolymer fibers, the tensile strength ofthe battery separator non-woven fabric can be increased while using alow blending ratio, and the tensile strength able to oppose the tensionof the battery production process can be maintained even if the basisweight is lowered.

The fiber length of the ethylene/vinyl alcohol copolymer fibers ispreferably 2 to 20 mm for the same reasons as the fiber length of thesemi-aromatic polyamide fibers.

In order to effectively spin fibers having high mechanical strength andresistant to the occurrence of sticking, the melt flow rate (MFR asdetermined in compliance with JIS K 7210 at a testing temperature of190° C. and testing load of 2.16 kgf) of the ethylene/vinyl alcoholcopolymer fibers is preferably 0.5 to 50 g/10 minutes, and in order tofurther improve ease of spinning, is more preferably 3 to 25 g/10minutes. On the other hand, the melt flow rate is more preferably 20g/10 minutes or less in consideration of mechanical properties.

In addition, the ethylene content in the ethylene/vinyl alcoholcopolymer is preferably 20 to 70 mol %, more preferably 30 to 55 mol %and particularly preferably 35 to 50 mol %. If the ethylene content isless than 20 mol %, problems occur with durability and so forth, and ifthe ethylene content exceeds 70 mol %, hydrophobicity becomesexcessively high. On the other hand, the content of the vinyl alcoholunit is preferably 30 to 80 mol %, more preferably 45 to 70 mol %, andparticularly preferably 50 to 70 mol %.

Although there are no particular restrictions on the production methodof ethylene/vinyl alcohol copolymer used in the present invention, itcan be efficiently produced by gelling ethylene/vinyl acetate copolymer.In addition, in consideration of ease of spinning and hot waterresistance, the average molecular weight of the ethylene/vinyl alcoholcopolymer is 500 to 5000, and more preferably about 800 to 3500.

Although ultrafine fibers composed of ethylene/vinyl alcohol copolymerfibers can be obtained by spinning those fibers only, a method ispreferably employed in which multi-component fibers havingethylene/vinyl alcohol copolymer as one of their components are spunfollowed by removing or separating the other components of the resultingmulti-component fibers. In particular, a method in which sea-islandfibers having ethylene/vinyl alcohol copolymer for their islandcomponent are spun, followed by removing the sea component of thesea-island fibers, is preferable due to the ease of thread production.

There are no particular restrictions on a polymer that is compound-spunor mix-spun with ethylene/vinyl alcohol copolymer provided it does notsubstantially impair the performance of the copolymer. Examples of suchpolymers include polyamide (preferably Nylon 6) that can be removed withan acidic aqueous solution, and an easily alkaline-removable polyestercapable of being removed with an alkaline aqueous solution. The use ofthe easily alkaline-removal polyester is preferable in consideration ofspinning ease, weight loss processing and costs.

C. Containment of Division Type Composite Fibers

In addition to semi-aromatic polyamide fibers and binder fibers composedof ethylene/vinyl alcohol copolymer, a non-woven fabric for an alkalinebattery separator of the present invention preferably contains divisiontype composite fibers formed from this semi-aromatic polyamide and atleast one type of polymer(s) selected from the group consisting ofpolyphenylene sulfide, polymethylpentene and polypropylene. As a result,together with enhancing absorption and retention of electrolyte, basisweight and thickness can be reduced without impairing leakageresistance, thereby making it possible to increase the capacity of analkaline secondary battery. In addition, the basis weight, thickness,tensile strength and pore diameter of the non-woven fabric can be easilycontrolled in the production of a non-woven fabric for an alkalinebattery separator.

A semi-aromatic polyamide in the division type composite fibers isobtained by a method previously described. The polyphenylene sulfide isof a linear type, and the polymethylpentene is poly-4-methylpentene-1and copolymers thereof. Examples of the copolymer include thoseresulting from copolymerization of 4-methylpentene-1 and one or morekinds of, for example, ethylene, propylene, butene-1, hexene-1,octene-1, setene-1, tetrasetene-1 and octadecene-1.

In addition, there are no particular restrictions on the compounded formin the fiber cross-sections of the division type composite fibers formedfrom semi-aromatic polyamide and at least one type of polymer selectedfrom the group consisting of polyphenylene sulfide, polymethyl-penteneand polypropylene provided the cross-sectional shape can be split afterspinning. For example, complex fibers can be used in which the shape ofthe mono-filament cross-section after splitting is wedge-shaped, of thebimetal type (strip-shaped) or a laminated combination thereof. Inconsideration of increasing leakage resistance, the monofilamentcross-sectional shape after splitting is particularly preferably of thebimetal type.

In consideration of ease of splitting, all of the components thatcompose the complex fibers are preferably split into two or more regionsby other components in the fiber horizontal cross-section, and the totalnumber of splits in the complex fiber horizontal cross-section (totalnumber of regions, total number of layers) is more preferably from 8 to20. In addition, in consideration of ease of splitting and ease ofspinning, each layer is preferably substantially continuous in thelengthwise direction of the fibers.

The fiber diameter of each region (layer) that composes the complexfibers is such that the mono-filament fineness is preferably 0.6 dtex orless and more preferably 0.3 dtex or less in consideration of liquidabsorption and liquid retention to electrolyte, ease of splitting, andseparation performance as a battery separator non-woven fabric, whilethe monofilament fineness is preferably 0.01 dtex or more inconsideration of not inhibiting unidirectional gas permeability. Thefiber length of the division type composite fibers is preferably 2 to 20mm for the same reasons as the fiber length of the semi-aromaticpolyamide fibers.

The blending ratio of the division type composite fibers is preferablysuch that they are contained at 5 to 30% by weight in a non-woven fabricfor an alkaline battery separator in consideration of liquid absorption,liquid retention, and gas permeability, and more preferably 10 to 20% byweight in consideration of leakage resistance. If the blending ratio isless than 5% by weight, the effects of lowering basis weight andreducing thickness are unable to be demonstrated as compared with anon-woven fabric composed of semi-aromatic polyamide fibers andethylene/vinyl alcohol copolymer fibers. On the other hand, if theblending ratio exceeds 30% by weight, although leakage resistance isimproved, charging and discharging characteristics decrease due toinhibition of gas permeability.

D. Containment of Non-Stretched Semi-Aromatic Polyamide Fibers

A non-woven fabric for an alkaline battery separator of the presentinvention can additionally be composed of a non-woven fabric containingnon-stretched semi-aromatic polyamide fibers.

Here, non-stretched polyamide fibers refer to fibers in which, forexample, crystallization and orientation are minimized as much aspossible to prevent the occurrence of a stretched orientation in aproduction process in which molten semi-aromatic polyamide resin isextruded from a nozzle, cooled to a solid, formed into threads and thentaken up by a roller. The semi-aromatic polyamide fibers of the presentinvention are products of heating and stretching these non-stretchedpolyamide fibers.

Since non-stretched polyamide fibers have numerous non-crystallinesections as compared with semi-aromatic polyamide fibers, and thesenon-crystalline sections are susceptible to deformation at temperaturesequal to or above the glass transition temperature, they can be used asbinder fibers of semi-aromatic polyamide fibers. In addition, sincenon-stretched polyamide fibers have superior hydrophilicity in the samemanner as the semi-aromatic polyamide fibers, a battery separator can beobtained that has high liquid retention.

The blending ratio of non-stretched polyamide fibers is preferably 1 to10% by weight with respect to the semi-aromatic polyamide fibers andethylene/vinyl alcohol copolymer fibers. If non-stretched polyamidefibers are added within this range, the liquid retention rate can beincreased without affecting battery life.

E. High-Strength Fibers

A non-woven fabric for an alkaline battery separator of the presentinvention can also be constituted by a non-woven fabric additionallycontaining high-strength fibers. This is because the use of a non-wovenfabric containing a combination of semi-aromatic polyamide fibers havingsuperior chemical stability such as heat resistance, oxidationresistance and others as well as superior adhesiveness withthermoplastic binder, and high-strength fibers having superiorhydrophilicity, alkaline resistance and mechanical strength makes itpossible to significantly reduce the defect rate during batteryproduction without causing problems such as tearing of the separator orshort-circuit of the electrodes during battery production.

High strength and high elastic modulus fibers having a tensile strengthof 15 cN/dtex or more, tensile elastic modulus of 400 cN/dtex or moreand rupture elongation of 10% or less are preferable for thehigh-strength fibers, examples of which include Kevlar (registeredtrademark), Xyron (registered trademark), Kuralon K-II (registeredtrademark) manufactured by Kuraray Co., Ltd. and Dainimer (registeredtrademark) fibers. As a result of containing high-strength fibers,rupture and short-circuit caused by stretching of the separator can beprevented in the case of high-speed winding.

High-strength fibers are preferably contained within the range of 1 to10% by weight with respect to the total amount of fibers. If within thisrange, the occurrence of interlayer separation or decreased mechanicalstrength of a non-woven fabric accompanying decreased adhesivenessbetween fibers can be avoided in a non-woven fabric for an alkalinebattery separator that contains semi-aromatic polyamide fibers andethylene/vinyl alcohol copolymer fibers.

Completely aromatic polyamide fibers are particularly preferable for thehigh-strength fibers, examples of which include meta-type completelyaromatic polyamide fibers such as poly-m-phenylene isophthalamide andpoly-m-xylene terephthalamide, or para-type completely aromaticpolyamide fibers comprising a resin component such as poly-p-phenyleneterephthalamide, poly-p-benzamide, poly-p-amidohydrazide, andpoly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide.Para-type completely aromatic polyamide fibers are particularlypreferable since they impart superior electrical insulation to a batteryseparator.

In addition, the fiber diameter of the high-strength fibers ispreferably 1.5 dtex or less and more preferably 1.0 dtex or less similarto the semi-aromatic polyamide fibers.

Basis Weight

Although there are no particular restrictions on the basis weight of anon-woven fabric for an alkaline battery separator, in order to achievethe object of higher capacity for an alkaline secondary battery, thebasis weight is preferably 45 g/m² or less and more preferably 40 g/m²or less. On the other hand, a basis weight of 30 g/m² or more ispreferable in consideration of leakage resistance.

In addition, although there are also no restrictions on thickness, inorder to lower the internal resistance, increase the amount of activematerial or increase the plate length, and achieve the object of highercapacity for an alkaline secondary battery, the thickness if preferably100 μm or less and more preferably 80 μm or less. On the other hand, thethickness is preferably 60 μm or more in consideration of leakageresistance.

Production Method of a Non-Woven Fabric for an Alkaline BatterySeparator

Next, a description is provided of a production method of a non-wovenfabric for an alkaline battery separator of the present invention.

The raw fabric of a non-woven fabric for an alkaline battery separatorcan be produced by a wet papermaking method, carding method, cross layermethod or other known method using each of the aforementioned types offibers.

Although the carding and cross layer methods are able to use fibershaving a long fiber length, it is difficult to form uniform rolls,alignment is poor and when observed with transmitted light, a spottedpattern is observed. Consequently, there is the problem of having to usea high basis weight in order to obtain a void diameter required toprevent short-circuit.

Moreover, although splitting using a needle punch method, water punchmethod or other means is required for splitting of division typecomposite fibers, since the needle punch method cannot be used at lowbasis weights and the fiber length is too long in the case of employinga dry method in the water punch method as well, there are problems withrespect to difficulties in splitting.

On the other hand, a wet papermaking method offers the advantage of afaster production rate was compared with the aforementioned methods, andfibers of different fiber diameters and multiple types of fibers can bemixed in an arbitrary ratio with a single device. Namely, a wideselection of fiber shapes such as staples and pulp can be used, fiberscan be used having fiber diameters ranging from ultrafine fibers of 7 μmor less to thick fibers, and raw fabric can be obtained that has muchbetter alignment as compared with other methods. Moreover, in thesplitting of division type composite fibers, division type compositefibers can be split completely in a refining step and dispersion stepwith a refining machine such as a pulper, high-speed mixer or beater.For these reasons, this method can be used to form raw fabrics having anextremely broad application range.

Therefore, a raw fabric of a non-woven fabric for an alkaline batteryseparator of the present invention is produced using a wet papermakingmethod. A uniform papermaking slurry is prepared by mixing 60 to 95% byweight of semi-aromatic polyamide fibers and 5 to 40% by weight ofethylene/vinyl alcohol copolymer fibers, dispersing in the water of apulper and stirring gently using an agitator. A wet paper roll is thenproduced from this papermaking slurry using a papermaking machine havingat least one wire such as a cylindrical papermaking machine, Fourdrinierpapermaking machine or inclined Fourdrinier papermaking machine, andafter adjusting the moisture content to 60 to 85%, the paper roll iscontacted with a Yankee dryer or blowing hot air from a hot air hooddryer provided on top of the Yankee dryer simultaneous to making surfacecontact with the Yankee dryer to dry at a temperature equal to or abovethe melting temperature of the ethylene/vinyl alcohol copolymer fibers.Furthermore, in the case of additionally containing division typecomposite fibers, the amount of those fibers is split in water using arefining machine to form a dispersed slurry in which ultrafine fibershave been formed followed by mixing this with the aforementionedsemi-aromatic polyamide fibers and ethylene/vinyl alcohol copolymerfibers.

Next, hydrophilic treatment is carried out to improve the electrolyteaffinity of the raw fabric obtained in this manner. Corona dischargetreatment, atmospheric pressure plasma treatment, fluorination treatmentor surfactant treatment can be used for the hydrophilic treatment.

Corona discharge treatment is a surface modification method thatgenerates a high-voltage corona discharge by providing a suitable gapbetween an electrode connected to a high-voltage generator and metalroll covered with silicone rubber and so forth followed by applying avoltage of several thousand to several ten thousand voltage at a highfrequency. The raw fabric obtained by the aforementioned method is thenpassed through the gap at a suitable speed causing the ozone or nitrogenoxide generated by the corona discharge to react on the surface of theraw fabric and resulting in the formation of carboxyl groups, hydroxylgroups and peroxide groups, thereby improving the affinity of theelectrolyte for the raw fabric.

Atmospheric pressure plasma treatment is a surface modification methodin which a gaseous composition substantially composed of helium or argonand oxygen is fed into a plasma reaction device having adielectric-coated electrode, in which a solid dielectric such aspolyimide, mica, ceramics or glass is provided on the surface of atleast one of a pair of opposing electrodes, to excite the plasma atatmospheric pressure and oxidize and etch the surface of a raw fabriclocated between the opposing electrodes followed to improve electrolyteaffinity.

Fluorination treatment is a surface modification method in which a mixedgas comprising fluorine gas diluted with nitrogen gas or argon gas andat least one type of gas selected from oxygen gas, carbon dioxide gasand sulfur dioxide gas is contacted with a raw fabric to form carboxylgroups, carbonyl groups and hydroxyl groups on the surface, therebyimproving electrolyte affinity.

Surfactant treatment is a surface modification method in which the rawfabric is impregnated with a solution of a nonionic surfactant such aspolyoxyethylene alkyl ether or polyoxyethylene alkyl phenol ether, orcoated or sprayed with this solution, followed by drying to improve theelectrolyte affinity of the raw fabric surface.

Next, the thickness of a non-woven fabric for an alkaline batteryseparator of the present invention is adjusted by calendaring treatmentusing a combination of rubber and rubber, steel and steel, steel andrubber, cotton and steel or cotton and cotton. Calendaring treatment canalso be carried out prior to hydrophilic treatment.

EXAMPLES

Although the following provides a more detailed explanation of thepresent invention using its examples, the present invention is notlimited to these examples. Furthermore, the term “parts” or “%” in theexamples refers to that based on weight unless specified otherwise.

Example 1

95% by weight of semi-aromatic polyamide fibers, in which 100 mol % ofthe dicarboxylic acid component comprising terephthalic acid and 100 mol% of the diamine component comprising 1,9-nonanediamine, and 5% byweight of ethylene/vinyl alcohol copolymer fibers were mixed, refined inthe water of a pulper and gently stirred using an agitator to prepare auniform papermaking slurry. The semi-aromatic polyamide fibers had amelt viscosity [1] as measured in conc. sulfuric acid at 30° C. of 1.0,a melting point of 317° C., a monofilament fineness of 0.5 dtex and afiber length of 5 mm, while the ethylene/vinyl alcohol copolymer fibershad an ethylene content of 44 mol %, MFR of 11 g/10 minutes,monofilament fineness of 0.01 dtex and fiber length of 3 mm. Thispapermaking slurry was then used to produce a raw fabric having a basisweight of 60.0 g/m² and width of 50 cm using a wet papermaking methodwith a cylindrical papermaking machine. Next, corona treatment wasperformed on both sides of this raw fabric using an electrode measuring20 mm wide by 600 mm, and a dielectric Hybalon measuring 3.2 mm,followed by calendaring treatment at a roll temperature of 60° C. toobtain a non-woven fabric for an alkaline battery separator having athickness of 150 μm.

Example 2

With the exception of using 95% by weight of semi-aromatic polyamidefibers, in which 100 mol % of the dicarboxylic acid component comprisingterephthalic acid, 50 mol % of the diamine component comprising1,9-nonanediamine, and the remaining 50% of the diamine componentcomprising 2-methyl-1,8-octanediamine, and 5% by weight ofethylene/vinyl alcohol copolymer fibers, the semi-aromatic polyamidefibers having a melt viscosity [η]as measured in conc. sulfuric acid at30° C. of 0.7, a melting point of 265° C., a monofilament fineness of0.5 dtex and a fiber length of 5 mm, and the ethylene/vinyl alcoholcopolymer fibers having an ethylene content of 44 mol %, MFR of 11 g/10minutes, monofilament fineness of 0.01 dtex and fiber length of 3 mm, anon-woven fabric for an alkaline battery separator was obtained in thesame manner as Example 1 having a basis weight of 59.5 g/m² andthickness of 151 μm.

Example 3

With the exception of using 80% by weight of semi-aromatic fibers of thesame composition as Example 2 having a monofilament fineness of 0.7 dtexand fiber length of 5 mm, and using 20% by weight of ethylene/vinylalcohol copolymer fibers having an ethylene content of 44 mol %, MFR of11 g/10 minutes, monofilament fineness of 0.08 dtex and fiber length of3 mm, a non-woven fabric for an alkaline battery separator was obtainedin the same manner as Example 1 having a basis weight of 53.5 g/m² andthickness of 125 μm.

Example 4

With the exception of using 60% by weight of the semi-aromatic polyamidefibers used in Example 2, and using 40% by weight of ethylene/vinylalcohol copolymer fibers having an ethylene content of 44 mol %, MFR of11 g/10 minutes, monofilament fineness of 0.4 dtex and fiber length of 3mm, a non-woven fabric for an alkaline battery separator was obtained inthe same manner as Example 1 having a basis weight of 55.2 g/m² andthickness of 125 μm.

Comparative Example 1

A Nylon dry non-woven fabric manufactured by JAPAN Vilene Co., Ltd.composed of Nylon 6 fibers and Nylon 66 fibers (carded type, basisweight: 63.5 g/m², thickness: 150 μm) was used as a non-woven fabric foran alkaline battery separator.

Comparative Example 2

A raw fabric having a basis weight of 58.3 g/m² and a width of 50 cm wasproduced by a wet papermaking method with a cylindrical papermakingmachine using 70% by weight of division type composite fibers having amono-filament fineness of 3.3 dtex, monofilament fineness after fiberspitting of 0.2 dtex (3.9 μm) and fiber length of 6 mm comprising highlycrystalline polypropylene fibers having an MFR at 230° C. of 20 g/10minutes and ethylene/vinyl alcohol copolymer having an ethylene contentof 38 mol % and MFR of 16 g/10 minutes, 15% by weight of core-sheathtype, heat-fused fibers having a monofilament fineness of 2.2 dtex(fiber diameter: 17.5 μm) and fiber length of 10 mm comprising a corecomponent in the form of highly crystalline polypropylene having an MFRat 230° C. of 20 g/10 minutes and a sheath component in the form ofethylene/vinyl alcohol copolymer having an ethylene content of 38 mol %and an MFR of 16 g/10 minutes, and 15% by weight of polypropylene fibershaving a monofilament fineness of 0.8 dtex (fiber diameter: 10.4 μm) andfiber length of 10 mm.

Next, this raw fabric was transported over a porous support in the formof 100 mesh stainless steel wire followed by water punching treatmentusing high-pressure columnar water flow to obtain a water-punchednon-woven fabric. The conditions of water punching treatment consistedof using three nozzle heads with the first head having a nozzle diameterof 120 μm and using water pressure of 70 kg/cm² at nozzle pitch of 0.6mm, the second head having a nozzle diameter of 100 μm and using waterpressure of 100 kg/cm² at a nozzle pitch of 0.6 mm, and the third headhaving a nozzle diameter of 100 μm and using water pressure of 130 kg/cmat a nozzle pitch of 0.6 mm, and a processing rate of 15.0 m/minute.Water punching treatment was first carried out on one side and thencarried out on the bottom side under the same conditions. Thiswater-punched non-woven fabric was then dried by blowing hot air at 110°C. from a hot air hood dryer. Next, corona discharge treatment wascarried out on both sides of the water-punched non-woven fabric followedfinally by calendaring treatment at normal temperature to obtain anon-woven fabric for an alkaline battery separator having a thickness of151 μm.

Example 5

With the exception of using 75% by weight of semi-aromatic polyamidefibers having monofilament fineness of 0.6 dtex and fiber length of 5mm, in which 100 mol % of the dicarboxylic acid component comprisingterephthalic acid, 50 mol % of the diamine component comprising1,9-nonanediamine, and the remaining 50% of the diamine componentcomprising 2-methyl-1,8-octanediamine, and 25% by weight ofethylene/vinyl alcohol copolymer fibers having an ethylene content of 44mol %, MFR of 11 g/10 minutes, mono-filament fineness of 0.01 dtex andfiber length of 3 mm, a non-woven fabric for an alkaline batteryseparator was obtained in the same manner as Example 1 having a basisweight of 36.5 g/m² and thickness of 85 μm.

Example 6

With the exception of adding 10% by weight of division type compositefibers to 70% by weight of the semi-aromatic polyamide fibers used inExample 2 and 20% by weight of ethylene/vinyl alcohol copolymer fibershaving an ethylene content of 44 mol %, MFR of 11 g/10 minutes,monofilament fineness of 0.08 dtex and fiber length of 3 mm, a non-wovenfabric for an alkaline battery separator was obtained in the same manneras Example 1 having a basis weight of 37.0 g/m² and thickness of 80 μm.Here, the division type composite fibers were laminated division typecomposite fibers having a monofilament fineness of 3.3 dtex,monofilament fineness after splitting of 0.3 dtex and fiber length of 5mm comprising the semi-aromatic polyamide of Example 2 and crystallinepolypropylene at a weight ratio of 7:3.

Example 7

With the exception of adding 20% by weight of the division typecomposite fibers of semi-aromatic polyamide and crystallinepolypropylene used in Example 6 to 60% by weight of the semi-aromaticpolyamide fibers used in Example 2 and 20% by weight of ethylene/vinylalcohol copolymer fibers having an ethylene content of 44 mol %, MFR of11 g/10 minutes, monofilament fineness of 0.08 dtex and fiber length of3 mm, a non-woven fabric for an alkaline battery separator was obtainedin the same manner as Example 1 having a basis weight of 36.7 g/m² andthickness of 82 μm.

Comparative Example 3

50% by weight of the division type composite fibers used in ComparativeExample 2, 30% by weight of core-sheath type, heat-fused fibers having amonofilament fineness of 0.6 dtex and fiber length of 3 mm comprising acore component in the form of polypropylene and a sheath component inthe form of high-density polyethylene, and 20% by weight ofpolypropylene fibers having a mono-filament fineness of 0.08 dtex andfiber length of 3 mm were mixed followed by refining in the water of apulper and gently stirring using an agitator to prepare a uniformpapermaking slurry. A raw fabric having a basis weight of 35.0 g/m² anda width of 50 cm was then produced using this papermaking slurry by awet papermaking method with a cylindrical papermaking machine. Next,corona treatment was performed on both sides of this raw fabric using anelectrode measuring 20 mm wide by 600 mm, and a dielectric Hybalonmeasuring 3.2 mm, followed by calendaring treatment at normaltemperature to obtain a non-woven fabric for an alkaline batteryseparator having a thickness of 80 μm.

The characteristic values of the non-woven fabrics for an alkalinebattery separator produced in Examples 1 to 7 and Comparative Examples 1to 3 were measured according to the measurement methods described below,and then evaluated according to evaluation methods. The characteristicvalues and performance evaluation results are shown in Tables 1 and 2.

<Measurement Methods>

[Basis Weight]

Basis weight was evaluated by adjusting to moisture equilibrium byallowing to stand in a test room at a temperature of 25° C. and relativehumidity of 55% followed by weighing 10 test pieces measuring 50 mm(direction of width)×200 mm (direction of length) with an electronicbalance to three decimal places, converting to weight per square meter(g/m²) and taking the average value.

[Thickness]

Thickness was evaluated by using a dial thickness gauge (micrometer)having a diameter of 6.3 mm to measure the thickness (μm) at sixdifferent locations each of five test pieces and taking the averagevalue.

[Alkaline Resistance]

Alkaline resistance was evaluated according to the weight loss rate (%)following alkaline treatment. The weight loss rate following alkalinetreatment was evaluated by sampling three test pieces measuring 10 cm×10cm from each sample, and after measuring the weight W (mg) after havingreached moisture equilibrium, immersing in an aqueous KOH solutionhaving a specific gravity of 1.30 equivalent to electrolyte and storingfor 20 days in an atmosphere at 90±2° C. After storing, the samples weretaken out followed by washing and drying until they reached the neutralpoint. The weight W₂ (mg) was then measured when the samples againreached moisture equilibrium to determine the weight loss rate (%)following alkaline treatment using the following formula 1.Weight loss ratio following alkaline treatment (%)=[(W−W₂)/W]×100  (Formula 1)[Tensile Strength]

Tensile strength was evaluated in accordance with JIS L 1096 for 10 testpieces measuring 50 mm (direction of width)×200 mm (direction of length)by pulling using a constant-speed drawing tensile tester underconditions of a clamping interval of 100 mm and pulling rate of 300mm/min, using the load value at breakage to represent tensile strength(kN/m) and taking the average value. A tensile strength within the rangeof 1.96 kN/m or more is preferable for use as a non-woven fabric for analkaline battery separator in order to withstand tension during thebattery production process and inhibit widening caused by stretching ofthe non-woven fabric.

[Pore Diameter]

Pore diameter was evaluated by measuring the maximum pore diameter andaverage pore diameter with the Coulter Porometer manufactured by CoulterElectronics.

<Evaluation Methods>

[Leakage Resistance]

200 coiled electrode assemblies were fabricated by using one each of apaste-type nickel hydroxide positive electrode (40 mm wide) using anickel foam material for the electrode collector and a sintered-typecadmium negative electrode (40 mm wide) using a nickel-plated punchingmetal, interposing a non-woven fabric for an alkaline battery separator(43 mm wide) of the aforementioned examples and comparative examplesbetween the electrodes, and winding using battery assembly machinery.The resistance between the positive and negative electrodes of theseelectrode assemblies was measured and resistance values of 500 kΩ ormore were treated as being indicative of a leakage defect. Leakageresistance was evaluated with a ◯ for leakage defects of 1% or less, a Δfor leakage defects of 2-3%, or an X in the case of leakage defects inexcess of 3%.

[High Rate Discharge Voltage]

Twenty size SUM3 sealed nickel-cadmium batteries having a nominalcapacitance of 0.7 Ah were fabricated by housing the aforementionedcoiled electrode assemblies in cylindrical metal cases followed byinjecting alkaline electrolyte consisting mainly of 7 N aqueouspotassium hydroxide solution containing 1 N lithium hydroxide andattaching sealing covers provided with a safety valve. In order totransform the batteries, the prepared batteries were repeatedly chargedand discharged four times consisting of charging for 15 hours at a 10hour rate at 25° C. and then discharging at a 1 hour current rate untilthe terminal voltage decreased to 0.8 V. Ten of the transformed sealednickel-cadmium batteries were then charged at a 0.5 hour rate current at25° C. followed by measurement of the average voltage when discharged ata 0.5 hour rate current to evaluate the high rate discharge voltage asan index in the case of assigning a value of 100 to a polyolefin-basednon-woven fabric for an alkaline battery separator.

[Low Rate Lifetime]

The remaining ten transformed sealed nickel-cadmium batteries were thenevaluated for low rate lifetime according to the number of charging anddischarging cycles consisting of charging for 30 hours with a 20 hourrate current at 70° C. and discharging with a 1 hour rate current untilthe terminal voltage decreased to 1.0 V. Low rate lifetime was evaluatedwith an X in the case of less than 80 cycles, a Δ in the case of 81 to150 cycles, or a 0 in the case of 151 cycles or more. TABLE 1Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example1 Example 2 Basis weight 60.0 59.5 53.5 55.2 63.5 58.3 g/m² Thickness μm150 151 125 125 150 151 Alkaline 2.3 2.9 2.9 3.6 33.2 2.1 resistance %Tensile 2.06 2.02 2.74 3.49 3.57 2.55 strength kN/m Max. pore 48.1 48.938.4 42.9 58.3 33.2 diameter μm Avg. pore 18.9 19.2 20.6 19.2 22.7 16.2diameter μm Leakage ◯ ◯ ◯ ◯ Δ ◯ resistance High rate discharge 108 107105 101 107 100 characteristics Low rate lifetime ◯ ◯ ◯ ◯ X ◯characteristics

TABLE 2 Example Example Example Comparative 5 6 7 Example 3 Basis weightg/m² 36.5 37.0 36.7 35.0 Thickness μm 85 80 82 80 Alkaline resistance %3.4 3.2 3.4 2.7 Tensile strength kN/m 2.16 2.35 2.27 1.67 Max. pore 50.534.1 27.4 34.9 diameter μm Avg. pore diameter μm 24.3 22.4 14.9 18.4Leakage resistance Δ ◯ ◯ X High rate discharge 105 105 105 100characteristics Low rate lifetime Δ ◯ ◯ ◯ characteristicsEvaluation

Table 1 shows a comparison of the characteristics of non-woven fabricsfor an alkaline battery separator having basis weights of 53 to 63 g/m²and thicknesses of 125 to 150 μm. Since the non-woven fabrics ofExamples 1 to 4 use semi-aromatic polyamide fibers having superiorchemical resistance and heat resistance, and ultrafine fibers ofchemically resistant ethylene/vinyl alcohol copolymers for the binderfibers, their alkaline resistance was far superior to the separatornon-woven fabric comprising the aliphatic polyamide fibers ofComparative Example 1, and about equal to that of the polyolefin-basedseparator non-woven fabric shown in Comparative Example 2. As a result,the low rate lifetime characteristics of Examples 1 to 4 are farsuperior to those of Comparative Example 1.

High rate discharge characteristics were such that the discharge voltagewas able to be increased for the polyamide-based separator non-wovenfabrics of Examples 1 to 4 as compared with the polyolefin-basedseparator non-woven fabric of Comparative Example 2.

Example 1 demonstrated superior alkaline resistance and high ratedischarge characteristics due to the higher degree of crystallinity thanExample 2.

Although Example 1 and Examples 3 and 4 depicted cases in which theblending ratio of semi-aromatic polyamide fibers was gradually decreasedwhile the blending ratio of the binder fibers was increased, despitetensile strength increasing the higher the blending ratio of the binderfibers, since high rate discharge characteristics decreased, it wasfound to be necessary that the blending ratio of the semi-aromaticpolyamide fibers be at least 60% by weight.

Table 2 shows a comparison of the characteristics of non-woven fabricsfor an alkaline battery separator having basis weights of no more than40 g/m² and thicknesses of about 80 μm. Although Example 5 depicts anon-woven fabric comprising 75% by weight of semi-aromatic polyamidefibers and 25% by weight of ethylene/vinyl alcohol copolymer fibers, asthe basis weight becomes smaller and the thickness of the non-wovenfabric decreases, although alkaline resistance and tensile strength areroughly equal to those of Example 1, leakage resistance and low ratelifetime characteristics are somewhat decreased. In contrast, inExamples 6 and 7 that contain division type composite fibers comprisingsemi-aromatic polyamide and polypropylene in addition to semi-aromaticpolyamide fibers and ethylene/vinyl alcohol copolymer fibers, bothleakage resistance and low rate lifetime characteristics are superior,and even at a basis weight of 40 g/m² or less and thickness of about 80μm, battery separator non-woven fabrics were able to be produced thatalso demonstrated high rate discharge characteristics. In addition, thehigh rate discharge characteristics of the separator non-woven fabricsobtained in Examples 6 and 7 were determined to be superior to those ofthe polyolefin-based separator non-woven fabric of Comparative Example3.

Example 8

5% by weight of non-stretched semi-aromatic polyamide fibers were addedto 90% by weight of semi-aromatic polyamide fibers and 5% by weight ofethylene/vinyl alcohol copolymer fibers, mixed and refined in the waterof a pulper and then gently stirred using an agitator to prepare auniform papermaking slurry. Here, the semi-aromatic polyamide fiberswere prepared from a dicarboxylic acid component in which 100% wasterephthalic acid and a diamine component in which 50% was 1,9-nonanediamine and the remaining 50% was 2-methyl-1,8-octane diamine, and had amonofilament fineness of 0.7 dtex, fiber length of 5 mm and meltingpoint of 265° C., while the ethylene/vinyl alcohol copolymer fibers hadan ethylene content of 44 mol %, fineness of 0.01 dtex and fiber lengthof 3 mm, and the non-stretched polyamide fibers were composed in thesame manner as the aforementioned semi-aromatic polyamide fibers and hada fineness of 1.6 dtex, fiber length of 5 mm and melting point of 265°C.

This papermaking slurry was then used to produce a raw fabric having abasis weight of 60.0 g/m² and width of 50 cm using a wet papermakingmethod with a cylindrical papermaking machine. Next, corona treatmentwas performed on both sides of this raw fabric using an electrodemeasuring 20 mm wide by 600 mm, and a dielectric Hybalon measuring 3.2mm, followed by calendaring treatment at a roll temperature of 60° C. toobtain a non-woven fabric for an alkaline battery separator having athickness of 150 μm.

Comparative Example 4

With the exception using core-sheath type, heat-fused fibers having afineness of 1.6 dtex and fiber length of 10 mm comprising a corecomponent in the form of polypropylene having a melting point of 155° C.and a sheath component in the form of polyethylene having a meltingpoint of 135° C., a non-woven fabric was obtained in the same manner asExample 1 having a basis weight of 60.0 g/m² and thickness of 150 μm.

These alkaline battery separators were evaluated as indicated below. Theresults are shown in Table 3.

<Measurement Methods>

[Liquid Retention Rate]

A test piece measuring 150 mm×100 mm was immersed for 1 hour in aqueousKOH solution having a specific gravity of 1.3 (concentration: 31% byweight) and then drained for 10 minutes. The weight of the test piecebefore treatment (W₀) and the weight of the test piece after treatment(W₁) were measured to determine the liquid retention rate (%) accordingto the following formula 2.Liquid retention rate (%)=[(W ₁ −W ₀)/W ₀]×100  (Formula 2)[Low Rate Lifetime]

This was measured and evaluated in the same manner as in Examples 1 to 7and Comparative Examples 1 to 3. TABLE 3 Liquid retention Low ratelifetime rate (%) evaluation Example 8 270 Δ Comparative 220 X Example 4

The alkaline battery separator of Example 8 demonstrated a higher liquidretention rate and superior battery life at 90° C. as compared withComparative Example 5.

Example 9

5% by weight of para-type completely aromatic polyamide fibers wereadded to 90% by weight of semi-aromatic polyamide fibers and 5% byweight of ethylene/vinyl alcohol copolymer fibers, mixed and refined inthe water of a pulper and then gently stirred using an agitator toprepare a uniform papermaking slurry. Here, the semi-aromatic polyamidefibers were fibers in which 100% of the dicarboxylic acid component wasterephthalic acid, 50% of the diamine component was 1,9-nonane diamineand the remaining 50% of the diamine component was 2-methyl-1,8-octanediamine, and having a monofilament fineness of 0.7 dtex, fiber length of5 mm, melting point of 265° C. and tensile strength of 3.7 cN/dtex,while the ethylene/vinyl alcohol copolymer fibers were fibers having anethylene content of 44 mol %, monofilament fineness of 0.01 dtex andfiber length of 3 mm, and the para-type completely aromatic polyamidefibers were fibers having a monofilament fineness of 1.3 dtex, fiberlength of 6 mm and tensile strength of 18 cN/dtex.

This papermaking slurry was then used to produce a raw fabric having abasis weight of 39.0 g/m² and width of 50 cm using a wet papermakingmethod with a cylindrical papermaking machine. Next, calendaringtreatment was carried out using a roll temperature of 200° C. followedby corona treatment on both sides of this raw fabric using an electrodemeasuring 20 mm wide by 600 mm, and a dielectric Hybalon measuring 3.2mm to produce a non-woven fabric having a basis weight of 39.0 g/m² andthickness of 100 μm that was used as an alkaline battery separator.

Example 10

As an example of a non-woven fabric not using high-strength fibers, 95%by weight of semi-aromatic polyamide fibers and 5% by weight ofethylene/vinyl alcohol copolymer fibers were mixed, refined in the waterof a pulper and then gently stirred using an agitator to prepare auniform papermaking slurry. This papermaking slurry was then used toproduce a raw fabric having a basis weight of 38.0 g/m² and width of 50cm using a wet papermaking method with a cylindrical papermakingmachine. Next, corona treatment was performed on both sides of this rawfabric using an electrode measuring 20 mm wide by 600 mm, and adielectric Hybalon measuring 3.2 mm followed by calendaring treatment ata roll temperature of 60° C. and adjustment of thickness to produce anon-woven fabric having a basis weight of 38.0 g/m² and thickness of 100μm that was used as an alkaline battery separator.

Here, the semi-aromatic polyamide fibers were the same as those used inExample 9, and the ethylene/vinyl alcohol copolymer fibers had anethylene content of 44 mol %, monofilament fineness of 0.08 dtex andfiber length of 3 mm.

Evaluation of the defect rate during battery production and a rapidcharging and discharging test were conducted on these fabrics accordingto the methods described below. Those results are shown in Table 4.

<Evaluation Methods>

[Evaluation of Defect Rate During Battery Production]

Coiled electrode assemblies were fabricated by using one each of apaste-type nickel hydroxide positive electrode (40 mm wide), using anickel foam material for the electrode collector, and hydrogen-occludingalloy negative electrode (40 mm wide), also using a nickel foammaterial, interposing an aforementioned alkaline battery separator (43mm wide) between the electrodes, and winding using battery assemblymachinery. After housing the coiled electrode assemblies in cylindricalmetal cases, alkaline electrolyte was injected consisting mainly of 7 Naqueous potassium hydroxide solution containing 1 N lithium hydroxideand sealing covers provided with a safety valve were attached to produce10,000 size SUM3 sealed nickel-hydrogen batteries having a nominalcapacitance of 1.8 Ah. Subsequently, a voltage of 240 V was appliedbetween the positive and negative electrodes and the defect rate (%)during production of 10,000 batteries was determined by defining thosebatteries having an electrical resistance of 1 kΩ or more as beingdefective.

[Rapid Charging and Discharging Test]

Ten size SUM3 sealed nickel-cadmium batteries were produced having anominal capacitance of 0.7 Ah using the same method as previouslydescribed. In order to transform the batteries, the batteries wererepeatedly charged and discharged four times consisting of charging for15 hours at 0.1 C and 25° C. and then discharging at a current of 1 Cuntil the terminal voltage decreased to 0.8 V. The transformed batterieswere then repeatedly charged and discharged using a cycle consisting ofcharging for 1.2 hours at a current of 1 C and discharging at a currentof 1 C until the terminal voltage decreased to 1.0 V to evaluate batterylife. Battery life was evaluated with an X in the case of less than 500cycles, a Δ in the case of 500 to 749 cycles, or a ◯ in the case of 750cycles or more. TABLE 4 Defect rate during Rapid charging and batteryproduction (%) discharging test Example 9 0.03 ◯ Example 10 0.12 ◯

Although the alkaline battery separator obtained in Example 10 wascomprised of semi-aromatic polyamide fibers and binder fibers in theform of ethylene/vinyl alcohol copolymer, and the adhesiveness with thebinder fibers was satisfactory, due to the low mechanical strength ofthe fibers, the strength of the non-woven fabric is low and the defectrate during battery production is somewhat high. However, in thealkaline battery separator obtained in Example 9, since thehigh-strength fibers improve mechanical strength, the non-woven fabrichas extremely superior mechanical strength, thereby making it possibleto significantly reduce the defect rate during battery production.Furthermore, stable battery operation was confirmed in both Examples 9and 10 in the rapid charging and discharging test at 90° C.

INDUSTRIAL APPLICABILITY

A non-woven fabric for an alkaline battery separator of the presentinvention is formed from a non-woven fabric comprising 60 to 95% byweight of semi-aromatic polyamide fibers formed from a mixture of adicarboxylic acid component of which 60 mol % or more is an aromaticdicarboxylic acid component, and preferably a terephthalic acidcomponent, and a diamine component of which 60 mol % or more is analiphatic alkylene diamine component and preferably a 1,9-nonane diaminecomponent or 2-methyl-1,8-octane diamine component, and 5 to 40% byweight of binder fibers in the form of ethylene/vinyl alcohol copolymerhaving a monofilament fineness of 0.01 to 0.5 dtex, having superioralkaline resistance in which the weight loss rate of the separatornon-woven fabric 20 days after an alkaline resistance test in aqueousKOH solution having a specific gravity of 1.30 at 90° C. is 5% or less.In addition, since the separator non-woven fabric of an alkalinesecondary battery has superior leakage resistance, low rate lifetime andhigh rate discharge characteristics, it can be used preferably as aseparator non-woven fabric of an alkaline secondary battery required tohave large-current discharge and higher capacity.

Moreover, a separator non-woven fabric of an alkaline secondary batteryadditionally comprising division type composite fibers formed from thissemi-aromatic polyamide and one type of polymer selected from the groupconsisting of polyphenylene sulfide, polymethylpentene and polypropylenecan be held to a maximum pore diameter of 50 μm or less and average porediameter of 20 μm or less even if the basis weight is 45 g/m² or lessand the thickness of 100 μm or less. As a result, capacity can beincreased even further.

In addition, as a result of additionally comprising non-stretchedsemi-aromatic polyamide fibers or high-strength fibers, a non-wovenfabric for an alkaline battery separator of the present invention isable to significantly reduce the defect rate during battery productionin the case of having reduced the electrolyte retention rate or basisweight.

Thus, since the present invention enables rapid charging andlarge-current discharging while also allowing thickness to be reducedthereby allowing higher capacity, it is preferable as a non-woven fabricfor an alkaline battery separator having superior alkaline resistance,thereby having extremely high industrial applicability.

1. A non-woven fabric for an alkaline battery separator comprisingsemi-aromatic polyamide fibers, prepared from a dicarboxylic acidcomponent in which 60 mol % or more of the dicarboxylic acid componentis an aromatic carboxylic acid component and a diamine component inwhich 60 mol % or more of the diamine component is an aliphatic alkylenediamine having 6 to 12 carbon atoms, and ethylene/vinyl alcoholcopolymer fibers, wherein the separator non-woven fabric has superioralkaline resistance in which the weight loss rate after 20 days is 5% orless in an alkaline resistance test at 90° C. in aqueous KOH solutionhaving a specific gravity of 1.30.
 2. The non-woven fabric for analkaline battery separator according to claim 1, wherein thesemi-aromatic polyamide fibers are 60 to 95% by weight, and theethylene/vinyl alcohol copolymer fibers are 5 to 40% by weight.
 3. Thenon-woven fabric for an alkaline battery separator according to claim 1,wherein the ethylene/vinyl alcohol copolymer fibers have a monofilamentfineness of 0.01 to 0.5 dtex.
 4. The non-woven fabric for an alkalinebattery separator according to claim 1, wherein the semi-aromaticpolyamide fibers are prepared from a dicarboxylic acid componentcomprising terephthalic acid and a diamine component comprising1,9-nonane diamine or a mixture of 1,9-nonane diamine and2-methyl-1,8-octane diamine.
 5. The non-woven fabric for an alkalinebattery separator according to claim 1, wherein the non-woven fabric foran alkaline battery separator additionally comprises division typecomposite fibers formed from the semi-aromatic polyamide and at leastone type of polymer selected from the group consisting of polyphenylenesulfide, polymethylpentene and polypropylene.
 6. The non-woven fabricfor an alkaline battery separator according to claim 5, wherein thecontent of the division type composite fibers is 5 to 30% by weightrelative to the total amount of fibers.
 7. The non-woven fabric for analkaline battery separator according to claim 1, wherein the non-wovenfabric for an alkaline battery separator additionally comprisesnon-stretched semi-aromatic polyamide fibers.
 8. The non-woven fabricfor an alkaline battery separator according to claim 7, wherein thecontent of the non-woven semi-aromatic polyamide fibers is 1 to 10% byweight relative to the total amount of fibers.
 9. The non-woven fabricfor an alkaline battery separator according to claim 1, wherein thenon-woven fabric for an alkaline battery separator additionallycomprises high-strength fibers.
 10. The non-woven fabric for an alkalinebattery separator according to claim 9, wherein the content of thehigh-strength fibers is 1 to 10% by weight relative to the total amountof fibers.
 11. The non-woven fabric for an alkaline battery separatoraccording to claim 1, wherein the basis weight is 45 g/m² or less, thethickness is 100 μm or less, the tensile strength is 1960 N/m or more,the maximum pore diameter is 50 μm or less, and the average porediameter is 20 μm or less.
 12. A method for producing a non-woven fabricfor an alkaline battery separator according to claim 1, which comprisesa step of preparing a dispersed slurry containing a mixture ofsemi-aromatic polyamide fibers and ethylene/vinyl alcohol copolymerfibers, a step of producing a raw fabric from the dispersed slurry usinga wet papermaking method, and a step of subjecting to hydrophilictreatment and calendaring treatment on both sides of the raw fabric. 13.The method for producing a non-woven fabric for an alkaline batteryseparator according to claim 12, wherein the dispersed slurryadditionally comprises a dispersed slurry to which division typecomposite fibers have been added that have been preliminarily split intoat least two types of ultrafine fibers with a refining machine.